How to print an array of ArrayList in Java?

Question

I have created a array of ArrayList but now I want to access its elements and sort them and print them, please help me to find out a way

  ArrayList<Integer>[] lists = (ArrayList<Integer>[])new ArrayList[20] ;
  for(int i=0;i<20;i++){
    lists[i]=new ArrayList<Integer>();
    lists[i].add(i+i*2);
    lists[i].add(i+i*3);
    lists[i].add(i+i*4);
    lists[i].add(i+i*5);
  }  
   System.out.println(lists);

output:-

[Ljava.util.ArrayList;@15db9742

So the problem is how to print an array in a readable form? – f1sh Sep 26 '16 at 17:44 — f1sh, Sep 26 '16 at 17:44
(let's duplicate this for future readers) – Sep 26 '16 at 18:12 — , Sep 26 '16 at 18:12

Nicolas Filotto · Accepted Answer · 2016-09-26T18:06:26.750

1

You need to use Arrays.toString(Object[]) to print the content of your array as next:

System.out.println(Arrays.toString(lists));

Arrays.toString(Object[]): Returns a string representation of the contents of the specified array. If the array contains other arrays as elements, they are converted to strings by the Object.toString() method inherited from Object, which describes their identities rather than their contents.

Using Arrays.toString(Object[]) to print the content of your array is enough in your case as an ArrayList is a subclass of AbstractCollection which overrides toString() to give a String representation of the collection in square brackets using a comma as value separator and here values are Integers.

edited Sep 26 '16 at 18:06

answered Sep 26 '16 at 17:46

Nicolas Filotto

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thanks it works but what if i want to modify an ArrayList at ith index of an array ? how to access? – Vijay Kumar Prajapat Sep 26 '16 at 17:59
`lists[n]` will return the n + 1 th element of your array – Nicolas Filotto Sep 26 '16 at 18:01
Oh damn !! , bye the way thanks – Vijay Kumar Prajapat Sep 26 '16 at 18:02

How to print an array of ArrayList in Java?

1 Answers1